Links require same ID type

**API Platform version(s) affected**: 3.0.7

**Description**
`Link`s require the same property type when following the example here: https://api-platform.com/docs/core/subresources/#company-employees

If the `id` type is a `string` on `Company`, it will fail if the `id` is type `UUIDv4` for example on `Employee`. The issue is caused because the type is retrieved from the last identifier in the URL, and not for the particular identifier.

**How to reproduce**
See the link above.

**Possible Solution**
```
--- /dev/null
+++ ../src/Doctrine/Orm/State/LinksHandlerTrait.php
@@ -118,6 +118,9 @@
$queryBuilder->join("{$previousAlias}.{$link->getToProperty()}", $joinAlias);

foreach ($identifierProperties as $identifierProperty) {
+ $associationTargetClass = $doctrineClassMetadata->getAssociationMapping($link->getToProperty())['targetEntity'];
+ $doctrineClassMetadata = $manager->getClassMetadata($associationTargetClass);
+
$placeholder = $queryNameGenerator->generateParameterName($identifierProperty);
$queryBuilder->andWhere("$joinAlias.$identifierProperty = :$placeholder");
$queryBuilder->setParameter($placeholder, $this->getIdentifierValue($identifiers, $hasCompositeIdentifiers ? $identifierProperty : null), $doctrineClassMetadata->getTypeOfField($identifierProperty));

```
**Additional Context**
I didn't submit this as a PR as I'm not sure if there is more to the code that maybe we need to change, but this did solve our issue.